Certain embodiments herein relate to printheads for use in inkjet printing, wherein the printheads are assembled with an adhesive compatible with ultraviolet curable inks. Also, described herein are methods of making such printheads.
Inkjet printing systems typically include one or more printheads having a plurality of inkjets from which drops of fluid (e.g., liquid or gel) ink are ejected toward a recording medium. The inkjets of a printhead receive ink from an ink supply chamber (manifold) in the printhead which, in turn, receives ink from a source such as an ink reservoir or an ink cartridge. Each inkjet includes a channel having one end in fluid communication with the ink supply chamber. The other end of the ink channel has an orifice or nozzle for ejecting/jetting drops of ink. An aperture plate of a printhead can have openings corresponding to the nozzles of the inkjets. An actuator is located along an ink channel near a nozzle to expel drops of fluid from the inkjet nozzles onto a recording medium. By selectively activating the actuators to eject ink drops as the recording medium and printhead assembly are moved relative to one another, the deposited drops can be precisely patterned to form particular text and/or graphic images on a recording medium.
Ultraviolet curable inks (e.g., fluid and phase change UV inks) permit increased printing speeds in inkjet printers, because they can be dried/set quickly in a controlled manner. UV inks can also be very durable. Formulations for UV inks (including UV curable phase change inks) are known in the art and can be manufactured using photoinitiators and mixtures of curable monomers and oligomers. Different types of UV inks can be used in different types of inkjet printers (e.g., piezoelectric inkjet printers, thermal inkjet printers, and acoustic inkjet printers).
Printheads used in the different types of inkjet printers can have a series/stack of plates, each plate performing an ascribed function within the printhead. A printhead assembly can, for example, include a piezoelectric transducer plate carrying PZT (lead zirconate titanate) slabs (or other actuator component plates), a stand-off plate, a circuit board, a manifold plate and a plate making up a compliant outer wall, among others. The stack for the printhead assembly can also include one or more adhesive layers that bond adjacent plates in the stacked assembly together. With direct marking print technologies, such as inkjet applications, the quality of print image resolution is very important. The quality of the printed image can be diminished when the structure of the ink channel or the stack of plates is deformed in the printhead.
The plates in a printhead stack can be formed of aluminum, stainless steel, gold-plated stainless steel, or plastics (such as, polyimides). In some assemblies, metallic plates are brazed together. However, some printheads have polymer adhesives that join metal and/or plastic plates of the stack. Some adhesives can result in squeeze-out, where the adhesive layer squeezes out from between two plates in the stack as the surfaces are bonded together. Incompatibility of an adhesive layer with ink (i.e., UV ink) being used or squeeze-out can deform the ink channel and lessen print quality. Further, the interaction between the ink (such as UV ink) and certain adhesive layers can weaken bonding between plates in the stack, which can cause structural failure of the printhead and reduce the printhead's operating life.
Achieving reliable adhesion between many different inkjet printhead layers and materials, particularly in the harsh environmental conditions found in current inkjet printhead uses, is a concern for device manufacturers. There is a need for adhesives to fix plates within a printhead stack together that are stable upon exposure to UV inks.